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On June 16, 2022, the U.S. Coast Guard’s Commander, Design and Engineering Standards Bureau (ENG-3) issued Maritime Safety Information Bulletin #05-22 (MSIB) for ships- cisterns.1 Specifically, the MSIB has authorized and approved double blockage and purge systems for inert gas systems on tankers that are designed, installed and operated in accordance with the 74 Convention for the Safety of Life at Sea ( SOLAS) (14) II-2/5.5 pursuant to 46 CFR §32.53-10(b). The significance of the MSIB is that ship owners and operators with SOLAS compliant double block and purge systems for inert gas systems on tankers do not need an approval for their system. by the Coast Guard Maritime Safety Center.
What is a backflow preventer for an inert gas system?
Large tankers regularly carry dangerous or flammable cargoes. The different grades and grades of oil cargo present in the cargo carry the inherent danger of producing flammable vapors and gases during the loading operation.2 In addition, flammable gas residues in an empty cargo hold are also an explosion hazard.3 Typically, inert gas systems designed to reduce explosions are equipped with an isolation valve; washing tower; demisting to absorb moisture; gas blower; Inert gas pressure reducing valve; deck seal; bridge isolation valve; pressure vacuum breaker; cargo tank isolation valve; mast riser; and security and alarm system.4
The inert gas system’s “non-return device” is a barrier that prevents hazardous and flammable cargo vapors from entering machinery spaces and other areas of the vessel that could cause an explosion. According to the Coast Guard’s MSIB, “The dual block-and-bleed valve arrangement isolates or blocks the return of gas from the cargo area to the engine room and allows any residual gas in the gas system to be purged.” inert”.5
The SOLAS amendment
Technical requirements for inert gas systems on board tankers are contained in the current version of 46 CFR Subchapter D, Subpart 32.53. These regulations, however, are obsolete as they require compliance with the provisions of SOLAS II-2 Regulation 62, which has since been superseded by SOLAS II-2 Regulation 5.5. The new SOLAS provision, Regulation 5.5, requires shipowners to comply with the International Maritime Organization (IMO) Fire Safety Systems (FSS). This new provision provides that vessels may use a dual isolation and bleed system in addition to a deck water seal.6
The MSIB clarifies that vessels equipped with a backflow preventer with a double block and bleed conforming to the FSS code are acceptable to the Coast Guard without the need for additional approval from the Coast Guard Maritime Safety Center.
5 Marine Safety Information Bulletin 05-22.
6 Amendment to Chapter 15 is contained in IMO Circular MSC.367(93).
The content of this article is intended to provide a general guide on the subject. Specialist advice should be sought regarding your particular situation.
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